Phorid flies that emerged from a Chronicle honeybee in the lab at S.F. State. Zombie bees have been found in 77 percent of the Bay Area hives checked.

The professor had warned us.

After several months of using a light lure to trap our Chronicle bees at night, researchers at San Francisco State University have found zombie bees in our hives.

In late July, a sample of our bees taken to the S.F. State lab proved to be infested with Apocephalus borealis, a small parasitic fly that lays its eggs inside the bee so its hatchlings devour the host from within.

The invasion causes the bee to have a neurological meltdown and exhibit strange behavior, such as flying at night toward light.

Eventually the bee dies, and the fly pupae emerge from the soft part of the bee's neck.

Which is exactly what happened after biology Professor John Hafernik and graduate research assistant Christopher Quock collected 18 bees from our rooftop apiary on their fourth visit.

Five days later, they spotted seven fly pupae that had emerged from one of our bees.

"I'm not surprised we found zombie bees, because we've found them in a majority of the hives we've looked at," Hafernik said.

The researchers have found zombie bees in 77 percent of the Bay Area hives they've checked, including colonies in Walnut Creek, Marin, Redwood City, on their own campus and now atop The San Francisco Chronicle. Apocephalus borealis has also been found in commercial hives in the Central Valley and in South Dakota.

San Francisco State just launched a citizen scientist website at www.zombeewatch.org to collect more data from backyard beekeepers.

What is unclear is whether honeybee colonies have been successfully living with the flies all along, or if this is a new threat that's growing.

Commonly known as the phorid fly, there are 4,000 species worldwide, but only a handful that attack honeybees, mostly found in Costa Rica, Mexico and Colombia. Apocephalus borealis are native to North America, first reported in Maine in 1924, and later Alaska and New Mexico - but those flies were attacking bumblebees and paper wasps.

So it was shocking when Hafernik and Quock discovered flies emerging from honeybees they collected at San Francisco State in late 2008, leading beekeepers to wonder if phorid flies are a major contributor to the annual 30 percent drop in the honeybee population known as colony collapse disorder.

To get closer to an answer, Hafernik and Quock are gluing glitter-size radio tags on campus bees to monitor the bees' comings and goings, with a laser beamed over the entrance to their laboratory hive.

The goal is to see whether parasitized bees are also leaving the hive during the day. They are trying to understand if bees are sacrificing themselves and saving the colony by abandoning it.

Right now, our Chronicle bees have what Hafernik describes as a "light infestation." But it could get worse.

In California, parasitism peaks in fall and early winter.

"There's nothing a beekeeper can do at this point until we know more about colony behavior and co-existence, or not, with the fly," Hafernik said.